Activation of macrophages (MO) by the Gram-negative bacterial product lipopolysaccharide (LPS) or Gram-positive bacteria initiate multiple signaling cascades and pro-inflammatory mediators important in the pathogenesis of septic shock. The latter play a major role in the pathogenesis of sepsis. LPS and the Gram-positive bacteria heat-killed Staphylococcus aureus (HK-SA) activate MO through Gi protein-coupled and Toll-like receptor (TLR) signaling pathways. Potential links between these signaling pathways are unknown. Gi protein-coupled and TLR signaling pathways are profoundly altered in the phenomenon of LPS tolerance (TOL). LPS TOL is induced by pre-exposure of ME) to low concentrations of LPS, which suppresses pro-inflammatory mediator production. HK-SA TOL induces a similar form of TOL. However, HK-SA TOL induces priming to LPS rather than cross TOL. These results prompted the hypothesis that Staphylococcus aureus induces homologous tolerance and priming to bacterial lipopolysaccharide through changes in heterotrimeric Gi proteins and Toll-like receptor-coupled signaling pathways. Two interrelated specific aims will test the hypothesis. Specific aim 1 will determine the effects of HK-SA and LPS induced homolgous TOL on signaling though Gi protein and TLR coupled pathways and to LPS mediator production. Specific aim 2 will determine the mechanisms whereby HK-SA TOL induced priming responses to LPS alters Gi protein-coupled and TLR signaling pathways and mediator.